Multi-head linear motors have been developed that can individually drive a plurality of movers by arranging the movers having the same size above a single stator as linear motors used for, for example, feeders mounted on semiconductor manufacturing equipment, electronic component mounting equipment, or tables of machine tools or the like. Such multi-head linear motors relate to a technique disclosed in Japanese Patent Application Laid-open No. 2001-211630.
In such multi-head linear motors, a mover constituting an armature includes a mover base and a plurality of armature coils collectively wound around an armature core and being in three-phase connection. On the other hand, a stator constituting a field is arranged so as to face the armature through a magnetic air gap and is constituted of a field yoke and a plurality of permanent magnets provided in the longitudinal direction of the field yoke, that is, in the so-called linear direction so as to alternately have different magnetic poles. A multi-head linear motor with cores having such a structure in which a plurality of movers having the same build are arranged above a single stator can move individual works mounted on the movers.
The structure of the mover for the multi-head linear motor with cores is described in detail below. For example, a structure in which a relationship basically determined with a magnetic pole number P of permanent magnet fields and an armature coil number M is a combination of P=2 and M=3 is developed as one set. In this case, the lengths of the movers having the same combination can be determined so as to correspond to works requiring different necessary thrusts by constituting the movers with one set composed of a small thrust mover and two sets composed of a large thrust mover whose length corresponds to the length of two of the small thrust movers. Thus, in the multi-head linear motor, a combination of minimum units of the magnetic pole number and the coil number is determined as one set, and the set number of the movers is changed depending on a necessary thrust for each of the movers to deal with the works.
However, a motor build may be unnecessarily enlarged with an arrangement of movers of a conventional linear motor when necessary thrusts for the movers largely differ from one another, for example, the large thrust mover has 1000 newtons and the small thrust mover has 100 newtons.